Lightweight spherical blast resistant container

ABSTRACT

This invention is a novel minimum weight and minimum volume blast resistant container. The container is made of a blast resistant, fiber reinforced, polymer resin matrix, composite material. The invention employs a novel construction configuration whereby the container is created by winding a collection of continuous reinforcing fiber filaments, called a tow, or winding a collection of tows called a tape, around a spherical tool or mandrel. Prior to winding, resin is applied to the tow or tape by immersion into a resin bath. Such an approach provides an optimized minimum weight and minimum volume solution by fully utilizing all the material in the part, whereby ultimate tensile strength can be simultaneously developed everywhere in the container.

BACKGROUND OF THE INVENTION

The invention relates to a minimum weight and minimum volume spherical container capable of resisting an internal explosive detonation without rupture due to bombs or other improvised explosive devices (IED's). The invention applies to storage or handling of IED's or explosive materials where a minimum weight and minimum volume storage container is required.

There are many situations where safe handling of explosives is desirable, but the explosive needs to be contained in the lightest, smallest container possible. Robotic devices are becoming a common method to retrieve suspected bombs or explosive materials. In order to minimize the load put on the robot, it is important that any container used for the explosives be as small and light as possible. Similarly, government agencies such as the Department of Defense, Federal Bureau of Investigation, or police departments desire to store explosives in the smallest volume possible to maximize the utility of their facilities. Explosive materials stored in military assets also should take up as little space and add as little weight as possible.

The general case of containers for explosives is covered in a copending application by the same inventor. It is the object of this invention to provide a solution to the special case of blast containment in the minimum weight/volume container

BRIEF SUMMARY OF THE INVENTION

The invention is a spherically shaped blast resistant container, constructed entirely or in part of a blast resistant composite material. In the preferred embodiment, the composite material is a fiber reinforcement in a polymer resin matrix.

In one aspect, the-polymer resin matrix is resistant to galvanic corrosion, solvents and chemical agents and exhibits a high specific strength, high specific modulus, high strain to failure, high fracture toughness and is not hygroscopic.

In another aspect the fiber reinforcement is treated with a special resin compatible sizing which develops a high specific laminate strength, high specific laminate modulus, high laminate strain to failure and a high laminate fracture toughness.

In another embodiment, the composite material is layered to form a laminate. In one version the layering may be accomplished by filament winding a tow of fibers or a collection of fiber tows, in the form of a strip or unidirectional tape, around a hollow spherical tool or mandrel. The winding is performed in a polar fashion to ensure uniform circumferential placement of fiber over the entire surface area of the spherical tool or mandrel.

In one embodiment the container is a blast containment vessel used for robotic handling of improvised explosive devices (IED's).

In another embodiment, the container is a minimum weight and minimum volume blast resistant explosives container for use in a building. In a further embodiment, the container is a minimum weight and minimum volume blast resistant explosives container for use in military assets.

In another embodiment the container may be used specifically for the safe storage of explosive materials in order to protect surrounding personnel and property from an accidental or unanticipated detonation of the explosives stored within the container.

In a further embodiment, in order to avoid personnel and property damage, the invention may be used by police, firemen or demolition teams as a portable container to safely detonate IED's or bombs planted by terrorists.

In a further embodiment, the invention is a method of constructing a blast resistant container, including providing collapsible tools which allow for forming of a sphere containing an opening, providing a tool for fabricating a door or hatch, fabricating and curing the sphere and hatch, and assembling the sphere and hatch into a completed container.

In a further embodiment of the method, the containers are constructed at least in part using a fiber reinforced, polymer resin matrix, composite. In one aspect, the composite container is fabricated by polar winding a resin immersed fiber tow around a spherical tool or mandrel. In another aspect, the composite container is fabricated by polar winding a strip of fiber tows around a spherical tool or mandrel

One embodiment of the invention involves the construction of a blast resistant container utilizing fiber reinforced polymer composite laminate skins in combination with core materials to form a sandwich type construction. Low density core materials may include, opened or closed cell foam, a honeycomb material, nomex, metal foam, or balsa wood. In a further embodiment of the invention, the tool or mandrel for the sphere is collapsible such that when the container is completed, the tool may be removed through a hatchway built into the container. In one embodiment the tool is inflatable, and may be removed upon curing by deflation.

In another embodiment, a non-circular doorway opening may be cut out from the side wall and an oversized doorway hatch may be inserted inside the container. The interior hatch is self sealing against the wall of the sphere by the internal overpressure developed by the explosive detonation.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description of how to make and use the invention will be facilitated by referring to the accompanying drawings.

FIG. 1 illustrates the problem solved by the invention.

FIG. 2 shows one of the preferred construction configurations of the invention.

FIG. 3 shows a sandwich construction of the invention.

FIG. 4 shows construction of the invention using a suitable forming tool.

DETAILED DESCRIPTION OF THE INVENTION

The inventor has produced a completely new concept for blast protection containers, enabled in part by employing very different materials than currently used for container applications. Current container materials such as thin aluminum or steel provide little or no blast protection. Conventional materials exhibit relatively low specific strength and/or specific modulus. Consequently, blast resistant containers constructed using conventional materials do not offer a weight efficient solution. A new class of materials enables a different approach. Such materials are similar to fiberglass in that they utilize a reinforcing fiber architecture, which is surrounded by a polymer resin matrix. The most effective version of composite construction utilizes materials which exhibit high compressive and tensile specific strengths and high compressive and tensile specific moduli. Specific strength is defined as the ultimate compressive (or tensile) strength of the material divided by its density. Specific modulus is the elastic compressive (or tensile) modulus of the material divided by its density. The polymer resin matrix is resistant to galvanic corrosion, solvents and chemical agents. The inventor has developed a particularly suitable version of the material, described in a co-pending application. In this version, the fiber reinforcement is treated with a special resin compatible sizing which develops a high specific laminate strength, high specific laminate modulus, high laminate strain to failure and high laminate fracture toughness. These materials have much higher resistance to blast per unit volume than metals.

Referring to FIG. 1, a spherical container 1, is shown containing explosives 2. If the explosives 2 detonate in the container 1, the blast expands radially outward as a spherical overpressure front. Thus a spherically shaped container is the ideal shape to contain a blast.

A blast resistant composite for containers can be fabricated as follows. A lay-up tool or mandrel in the shape of the container is required. For the case of a sphere, the tool must be removed from the interior of the container after the container is fully cured. A spherical tool may be achieved by inflating a membrane like balloon in the shape of a sphere or by casting a spherical shape that may be dissolved by water or melted by heat, after the composite winding has fully cured. A suitable fabrication method is described below. A collection of continuous fiber filaments, known as a tow of fibers, is immersed in a resin bath. The wet tow is wound in a circumferential fashion around the aforementioned tool or mandrel. The reinforcement tow is continuously wrapped around the tool (mandrel) in multiple angles around the sphere until the required laminate thickness is achieved. The winding is vacuum bagged using a compressor to draw vacuum. A Convection Oven or Autoclave is used for curing the bagged winding. The Oven consists of insulated walls and a heater with a recirculating forced air blower. The Autoclave is a pressure vessel which permits curing at elevated pressure and temperature.

The composite may also be produced by winding a strip of tows (i.e. unidirectional tape) when the diameter of the spherical tool or mandrel is large in comparison to the width of the tape. This permits a greater deposition rate of reinforcing fiber onto the tool or mandrel which results in increased production rates, compared to single tow or filament winding. Curing of the winding may be accomplished by oven or autoclave as previously described.

AS shown in FIG. 1, the detonation of an explosive 2 inside a container 1 creates a spherical overpressure wave front. A spherical overpressure wave requires three dimensional resistance. A fundamental design principle in the containment of explosive detonations states that the greater the interior container volume (relative to the volume of explosive) the lower the a real density required to prevent container rupture (where a real density is defined as the weight per unit surface area of the container). However, container weight is the product of a real density and container surface area. Consequently, the optimum i.e. lightest container geometry for blast mitigation maximizes container internal volume while simultaneously minimizing container surface area. The geometry which best achieves this characteristic is a sphere. Circumferential hoop stresses are developed in the winding direction of the fiber reinforcement so the filaments are wrapped in a multitude of angles around the spherical tool to insure that hoop containment is achieved.

The spherical container is particularly well-suited to robotic explosive handling, since the minimum volume/weight characteristics of the spherical shape minimize the load on the robotic handler. Also, police, firemen or demolition teams may use the invention as a lightweight portable container to safely detonate abandoned or concealed terrorist bombs or IED's. The invention may also be used to safely store explosives where accidental or unanticipated detonation will not damage surrounding personnel or property, such as in facilities, warships or vehicles.

FIG. 2 illustrates the invention. A hollow spherical container 1 is produced using a composite material as described above. The container may be stored on a pedestal or support 3. A non-circular (e.g. elliptical) doorway 4 opening may be cut from the container wall, and an oversized doorway hatch, which is a section of spherical wall made of the same or equivalent blast resistant material, may be inserted inside the container. As long as the doorway opening is not a circular shape, an internal hatch geometry may be designed to fit through the doorway opening. The surface area of the internal hatch is made to be greater than the surface area of the doorway opening. Such a configuration develops a self-sealing mechanism as the perimeter of the hatch presses against the inside surface of the container side wall when the container is pressurized by explosive detonation.

FIG. 3 shows the construction of a blast resistant container utilizing fiber reinforced polymer composite laminate skins in combination with core materials to form a sandwich type construction. An inner layer 5 of the blast resistant composite may be formed. Low density core materials 6 may be machined and bonded to the inner layer 5. Low density core materials may include but not be limited to, opened or closed cell foam, a honeycomb material, nomex, metal foam, balsa wood, etc. Optionally an outer layer 7 of blast resistant composite may be wound around the low density core material 6.

In another approach to creating a blast resistant door, a section of the core material panels 6 is eliminated such that a gap exists between a part of 5 and 7. A doorway opening may be cut out through both layers on the side of the container where the gap was created by the elimination of part of 6. This gap may be used to accommodate a guillotine or sliding door which completely covers an interior footprint larger than the door opening

In order to achieve better resistance to blast, a continuous overlapping application of the composite material over the entire surface area of the tool is desired during construction. Also, in order to achieve minimum weight the tool must be removed from the container once the container is completely cured. A doorway may be left in the container wall, but preferably, to allow for continuous application of reinforcement tows, the doorway should be cut out. As shown in FIG. 4, a tool 8 can be made collapsible to size 9 which can be removed from the door. Alternatively, the tool can be made of a material which will dissolve in water or melt at elevated temperature allowing easy removal of tooling material after an opening is cut into the fully cured part. Also, an inflatable membrane or balloon may be used as a tool and deflated for removal through the doorway. 

1. A spherically shaped blast resistant container, constructed entirely or in part of a blast resistant composite material.
 2. The container of claim 1 wherein the composite material is a fiber reinforcement in a polymer resin matrix.
 3. The fiber reinforcement and polymer resin matrix of claim 2 wherein the fiber reinforcement and the polymer resin matrix are resistant to galvanic corrosion, solvents and chemical agents and exhibit a high specific strength, high specific modulus, high strain to failure, high fracture toughness and is not hygroscopic.
 4. The fiber reinforcement of claim 2 wherein the fiber reinforcement is treated with a special resin compatible sizing which develops a high specific laminate strength, high specific Laminate modulus, high laminate strain to failure and a high laminate fracture toughness.
 5. The container of claim 2, wherein the composite material is layered to form a laminate.
 6. The container of claim 1 wherein the container is used for robotic handling of explosives or improvised explosive devices (IED's).
 7. The container of claim 1 wherein the container is a minimum weight, minimum volume explosives container for use where minimum weight and/or volume is essential.
 8. The container of claim 1 wherein the container is a minimum weight, minimum volume explosives container for use in Military or commercial land, sea or air assets.
 9. The container of claim 1 wherein the container is a storage unit for explosive materials in order to protect the surrounding personnel and property from an accidental or unanticipated detonation of the explosives stored within the container.
 10. The container of claim 1 wherein the container is a portable container to safely detonate bombs or IED's.
 11. The container of claim 1 wherein core materials are placed between inner and outer walls of the composite.
 12. The container of claim 11 wherein, when assembled, the core material forms a sandwich consisting of an inner wall, the core material and an outer wall.
 13. The container of claim 11 wherein the possible core materials include, opened or closed cell foam, a honeycomb material, nomex, metal foam, or balsa wood.
 14. The container of claim 1 wherein a non-circular opening is cut into the container wall, and an oversized composite door is made to seal the opening from the inside.
 15. The container of claim 11 further comprising; at least one section of wall with a portion of empty space instead of core material, a door cutout through the wall of the container in the region with no core material; and, an internal door in the empty space which completely seals the door opening when in the closed position.
 16. The container of claim 15 where the door is a guillotine door.
 17. The container of claim 15 wherein the door is a sliding door.
 18. The container of claim 15 including door retainers to prevent movement of the door.
 19. A method of constructing a spherical blast resistant container, comprising: providing a collapsible and/or removable tool which allows for forming of a spherical shape made from a blast resistant composite material, making a doorway in the container wall. providing a tool for making a door of blast resistant composite material fabricating and curing the sphere and hatch; and, assembling the door and sphere into a completed container.
 20. The method of claim 19 wherein the containers are constructed at least in part using a fiber reinforced, polymer resin matrix, composite.
 21. The method of claim 20 wherein the reinforcement is a collection of fiber filaments, commonly referred to as fiber tow, whereby resin is applied to the fiber tow by immersion into a resin bath.
 22. The method of claim 20 wherein the reinforcement is a collection of fiber tows comprising a tape or band of reinforcement fibers whereby resin is applied to the tape by immersion into a resin bath.
 23. The method of claim 19 wherein the spherical tool is collapsible, and is removed through the door when the sphere is fully cured.
 24. The method of claim 19 wherein the spherical tool is inflatable, and is deflated and removed through the door when the sphere is fully cured.
 25. The method of claim 19 wherein the spherical tool is left in the container and becomes part of the structure.
 26. The method of claim 19 wherein the spherical tool may be dissolved (using water or other agent) or melted at elevated temperature, and then removed via the cutout doorway, after the part is fully cured. 